Method of consolidating incompetent formations



United States Patent O 3,454,959 METHOD OF CONSOLIDATING INCOMPETENT FORMATIONS John F. Muirhead, Jr., Oakmont, and Joseph L. Pekarek, Penn Hills Township, Allegheny County, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware N Drawing. Filed Sept. 29, 1967, Ser. No. 671,553 Int. Cl. E2lb 33/ 13 US. Cl. 166288 8 Claims ABSTRACT OF THE DISCLOSURE A well having casing set into an unconsolidated formation is completed by making a single perforation in the casing in the interval of the unconsolidated formation, displacing an aqueous liquid from the well through the opening into the surrounding formation to render the aqueous fluid in the formation mobile, producing sand into the well, displacing a liquid capable of setting to form a solid that will bond the particles together through the opening into the surrounding formation, and treating the liquid displaced into the surrounding formation to cause it to solidify to bond the particles of the formation together. Resin-forming liquids and solutions forming devitrifiable glasses are disclosed as suitable liquids capable of forming a solid that will bond the particles into a mass of adequate strength.

This invention relates to a method of completing wells and more particularly to a method of completing oil and gas wells in unconsolidated sands to provide wells of highflow capacity.

The sands in many oil and gas reservoirs are unconsolidated or only loosely bonded together. On production of fluids from those sands, sand flows into the well where it may plug the Well or, if the reservoir is under a high pressure whereby the fluids flow through the well at a high velocity, cause serious erosion of well equipment. Either plugging or erosion of well equipment makes necessary expensive work-over or repair of the well.

Many different methods have been developed in an effort to solve the problems arising from unconsolidated sands. One method is to set a screen in the well and pack gravel around the screen to form a permeable sleeve that will filter sand particles from fluids flowing into the well. Another method is to consolidate the formation by bonding together the particles of the formation with a suitable cementing material such as an organic resin.

In the treatment of wells for sand consolidation or chemical stimulation, it has been recognized that it is preferable to limit the area of the well through which treating compositions are displaced from the well into the formation. Because of the tendency of treating fluids to channel through the formation, elfective treating of longexposed intervals of the formation or through multiple perforations is frequently ineffective and the cause of failures in the treatment. In spite of the disadvantages in treating long exposed formations, most well treatments have been over a relatively long interval such as in exposed borehole below the casing or through perforations extending over a substantial length of the casing because of the low productivity of wells having a single limited opening exposed to the formation.

This invention resides in a method of completing a well to provide a well of high-flow capacity in which casing is set through an unconsolidated productive formation and a single opening is made in the casing to provide access to the productive formation. Water is displaced through the opening into the formation to loosen ice the unconsolidated sand, and thereafter pressure within the well is reduced to produce a small amount of sand into the well. The unconsolidated sand is then treated through the opening to consolidate the sand by any of the methods of sand consolidation.

The well to be treated by this invention is drilled into the productive sand by any conventional drilling method. Ordinarily the conventional rotary drilling method in which a drilling mud is circulated down a well through drill pipe and back up through the annulus surrounding the drill pipe to carry cuttings from the well is used. In the rotary drilling method, the sands immediately adjacent the borehole wall are usually damaged by the drilling mud which is as at a higher pressure than the fluids in the formations drilled. A filter cake of drilling mud solids is built on the borehole wall and liquids and soluble chemicals in the liquid portion of the drilling mud that pass through the filter cake into the formation frequently further damage the sands, for example, by causing swelling of clays.

After the borehole has been drilled to the desired depth into the productive formation, casing is run into the well and cemented in place in the conventional manner. Liquids from the cement encircling the casing may cause further damage to the formation. The casing is then perforated at the desired level in the productive formation by any desired perforating means. Ordinarily explosives in the form of shaped charges are used for the perforation. High-velocity jets of abrasive-laden fluids and mechanical perforating devices also can be used to make the desired opening.

It is'important to this invention that there only be a single opening through the casing into the formation to be treated. It is important to this invention that a controlled amount of sand flow into the well. If there is more than one opening, sand and treating materials may flow only through one of the openings. The term single opening does not include a single long continuous exposed section of the borehole wall such as might exist below the casing. It does include a single opening in casing at a single level as may be made by a shaped charge of the type used as a casing cutter. A single perforation in the casing is preferred because of the certainty in treatment through the single opening.

After the single opening has been made, water is displaced into the formation to increase the water concen tration in the formation surrounding the single opening to a concentration at which the Water is mobile. The sand in that portion of the formation is made fluid by the injected water and flows readily into the Well on a small reduction in pressure in the well to give a small pressure drop from the formation into the well. Flow of sand through the formation to the opening is essential to provide sand adjacent the opening in the casing. That sand can then be consolidated to form a permeable structure. In the absence of the displacement of water, the sand particles break from the formation. and leave a cavity outside the casing. The large area of a cavity presents the same problem as multiple perforations of uniform treatment over the exposed face. The amount of water displaced into the formation should be adequate to make the sand fluid throughout the area damaged during the drilling and well completion operations. Ordinarily sands are damaged for distances as high as two to three feet, but may range as high as ten feet, from the borehole wall. The amount of water displaced into the formation may vary from as little as about one barrel to as much as 10 to 15 barrels or even more. It is important that the injected water not damage the formation; hence, in most instances a concentrated solution of salt water is displaced into the formation to minimize swelling of clays.

After displacement of water into the well, the pressure within the well is reduced and a small amount of sand is produced into the well. Ordinarily about one to five cubic feet of sand is allowed to flow into the well by reduction of the pressure within the well to slightly below the formation pressure. If the single opening into the formation is in the form of several closely spaced openings, as much as to cubic feet of sand may be allowed to flow into the well. The increased fluidity of the sand resulting from the injection of water allows close control of the amount of sand flowing into the well. If water is not displaced into the formation, a large pressure drop is required to initiate the sand flow with a consequent loss of control and increased danger of a blowout.

It is not contemplated that any cavity is created in the formation immediately outside of the casing. The damaged sand closest to the casing flows into the well and is replaced with undamaged sand flowing from farther back in the formation toward the well to produce a zone of increased porosity and permeability outside of the opening in the casing. The sand produced into the well is removed by suitable means such as circulation of liquid in the well or swabbing.

It may be desirable to determine whether or not effective removal of damaged sand has been accomplished before consolidating the sands. That determination can be made by measuring the rate at which a liquid can be displaced into the well at a given pressure to determine the injectivity of the well. It has been found that the injectivity of the well gives an accurate indication of the productive capacity of the well.

After removal of the sand from the well, the formation adjacent the single opening can be consolidated by any of the many consolidation techniques that have been suggested for bonding particles of unconsolidated sands together. Many different resins have been recommended as particle bonding materials. Typical of such resins are phenol-formaldehyde resins and epoxy resins. In the usual resin-forming technique, resin-forming liquids are displaced into the formation. Setting of the resin-forming liquid to form the resin may be accomplished by the passage of time, heating the formation, or injecting a catalyst or a reactant into the impregnated formation. Frequently it is desirable to treat the formation prior to displacement of resin-forming liquid into it to insure wetting of the sand particles with the resin-forming liquid. In many instances, it is also desirable to follow the impregnation of the sand with a fluid that will displace the resin-forming liquid from the interstices between the sand particles before the setting of the liquid to form the resin.

A preferred sand consolidation method which may be used in this invention is the solder glass method described in U.S. Patent No. 3,332,490 entitled Aqueous Solutions of Devitrifiable Glasses, Methods of Using, and Products Thereof. In that method the sands are first treated to remove oil. Such treatment may involve the displacement of an aqueous solution of a surfactant from the well into the formation. A preferred method of treating is to lower a burner into the well, ignite the burner, and burn the sand clean of oil as described in U.S. Patent No. 3,332,490. A solder glass solution, for example, an aqueous solution containing 10.2 percent lead oxide, 1.6 percent zinc oxide, 1.4 percent boric acid, .324 percent silicon dioxide, 28.9 percent sodium silicate, 8.9 percent sodium hydroxide, and 48.9 percent water is displaced down the well and into the formation. All of the percentages are by weight. Air is displaced down the well and into the formation to remove liquid from within the casing and establish permeability in the formation surrounding the opening in the casing. A burner positioned near the opening in the casing is ignited and the temperature gradually increased to 1200 F. to drive out the water of solution and melt the glass. Heating is continued for six hours at 1200 F. to cause substantially complete devitrification.

Before treatment Barrels Tubing head per min. pressure, p.s.i.

After treatment Barrels Tubing hood per min. pressure, p.s.i.

Under the column labeled Before treatment the number of barrels of salt water injected per minute and the tubing head pressure on the salt water are listed. Under the column After treatment the injectivity in barrels per minute of salt water and the tubing head pressure after displacing water into the formation and producing sand and before consolidation of the formation with the solder glass treatment described in Patent No. 3,332,490 are listed. In Well A the treatment resulted in the rate of injection increasing 300 percent even though the pressure applied on the liquid was reduced to less than /3 of the pressure applied before the treatment. In Well C the rate of injection was increased approximately 900 percent even though the tubing head pressure was reduced from 1400 to 450 p.s.i. Air injectivity tests made before and after the consolidation with solder glass indicated that the increased injectivity was retained.

We claim:

1. A method of completing a well having casing set in an unconsolidated formation comprising making a single opening in the casing at the desired level in the unconsolidated formation, displacing an aqueous liquid compatible with the formation through the opening and into the formation in an amount adapted to increase the concentration of aqueous liquids in the formation adjacent the opening to a concentration at which the aqueous liquid is mobile, reducing the pressure within the formation and producing sand into the well, and thereafter bonding together particles of sand in the formation adjacent the opening.

2. A method as set forth in claim 1 in which the aqueous liquid is salt water.

3. A method as set forth in claim 1 in which bonding of the formation is accomplished by injecting through the opening into the formation a liquid capable of forming a solid to bond particles of the formation, and treating said liquid capable of forming a solid to cause bonding of the particles.

4. A method as set forth in claim 1 in which bonding is accomplished by injecting through the opening into the formation a liquid capable of setting to form an organic resin, and treating the liquid to cause formation of the resin.

5. A method as set forth in claim 1 in which setting is accomplished by displacing through the opening into the formation adjacent thereto a solution of devitrifiable glass, removing the solvent from the solution, and heating the formation to a temperature to cause melting and devitrification of the glass.

6. A method as set forth in claim 1 in which the bonding is accomplished by treating the formation to render the particles therein wettable by a liquid capable of forming a solid to bond the particles of the formation, displacing a liquid capable of forming a solid into the formation, displacing an inert fluid into the formation to remove liquid capable of forming a solid from the interstices therein and establish permeability in the formation,

and treating the formation to cause formation of solid bonding the particles of the formation.

7. A method of completing a well having casing set into an unconsolidated formation comprising making a single perforation in the casing at the desired level in the unconsolidated formation, displacing an aqueous solution from the well into the formation in an amount adequate to render mobile aqueous liquids in the formation for a distance of at least two feet from the perforation, reducing the pressure in the well and producing at least one cubic foot of sand into the well, heating the formation adjacent the perforation to remove oil therefrom, displacing a solution of a devitrifiable glass through the perforation and into the formation, displacing a gas through the perforation and into the formation to establish permeability therein, and heating the formation to melt and devitrify the glass.

6 8. A method as set forth in claim 7 in which 1-10 barrels of aqueous solution is displaced through the single perforation before producing sand.

References Cited UNITED STATES PATENTS 2,823,753 2/1958 Henderson et a1. 166-33 X 3,153,449 10/1964 Lebourg 16621 3,292,701 12/1966 Goodwin et a1. 16625 3,302,718 2/1967 Prats et a1. 16 633 3,327,783 6/ 1967 Ayers 166-33 3,332,490 7/1967 Burtch et al. 16629 STEPHEN J. NOVOSAD, Primary Examiner.

US. Cl. X.R. 166295 mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 454, 959 Dated July 8, 1969 Inventor(s) John F. Muirhead, Jr. and Joseph L. Pekarek It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

[' Column 4, lines 45 and 46, cancel "formation" and insert in lieu thereof -well-.

Column 4, line 62, cancel "setting" and insert in lieu thereof -bonding-O SIGNED AND SEALED MAY 121970 .Attest:

Edward M. FletchcJ'l. g 1M E. sammma, m.

omis 1 Attesting Officer 5 nts 

